• Journal of the Korean Ceramic Society
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• v.34 no.6
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• pp.645-651
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• 1997

Tetragonal zirconia polycrystals (TZPs) doped with $Y_{2}O_{3}$ and $Nb_{2}O_{5}$ were prepared by the conventional sintering to enhance fracture toughness and phase stability of TZPs without controlling the grain size. TZP composites were obtained by adding the transformable TZP to the non-transformable TZP in wt%. The monolithic tetragonal $ZrO_2$, same as the composite composition containing 15 wt% transformable TZP, sintered at $1550^{\circ}C$ for 10h in air, exhibited the fracture toughness of 9$MPam^{1/2}$ and no low-and high-temperature degradation at temperatures in the range of 220 to $1000^{\circ}C$ for 100h in air. The corresponding single composition was 90.24 mol% $ZrO_2$-5.31 mol% $Y_{2}O_{3}$-4.75 mol% $Nb_{2}O_{5}$. The microstructure observation revealed that the t-$ZrO_2$ grains grew grandually with sintering time and no microcraking and twinning were observed.

• Korean Journal of Materials Research
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• v.24 no.2
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• pp.111-115
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• 2014

Titanium and its alloys are useful for implant materials. In this study, porous Ti-Nb-Zr biomaterials were successfully synthesized by powder metallurgy using a $NH_4HCO_3$ as space holder and $TiH_2$ as foaming agent. Consolidation of powder was accomplished by spark plasma sintering process(SPS) at $850^{\circ}C$ under 30 MPa condition. The effect of high energy milling time on pore size and distribution in Ti-Nb-Zr alloys with space holder($NH_4HCO_3$) was investigated by optical microscope(OM), scanning electron microscope(SEM) & energy dispersive spectroscopy(EDS) and X-ray diffraction(XRD). Microstructure observation revealed that, a lot of pores were uniformly distributed in the Ti-Nb-Zr alloys as size of about $30-100{\mu}m$ using mixed powder and milled powders. In addition, the pore ratio was found to be about 5-20% by image analysis, using an image analyzer(Image Pro Plus). Furthermore, the physical properties of specimens were improved with increasing milling time as results of hardness, relative density, compressive strength and Young's modulus. Particularly Young's modulus of the sintered alloy using 4h milled powder reached 52 GPa which is similar to bone elastic modulus.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.29 no.10 s.241
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• pp.1407-1415
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• 2005

Strength change of an over-aged A12024 material was studied after being subjected to stages of severe plastic deformation by ECAP (Equal Channel Angular Pressing). Various kinds of strength value were measured using the conventional tensile test, Rockwell and Vickers hardness and the SP (small punch) test Due to limitation of the specimen size, tension test in transverse direction could not be conducted. Hence, SP test was employed for assessing the strength in transverse direction. Based on TEM observation the measured strength characteristics were explained based on the relation between microstructure, dislocation and strength. As the number of ECAP pass increases, the strength of A12024 was also increased. However, considerable change of strength, which is generally predicted, was not observed in this study. For the strength in transverse direction even decrease of the strength was observed after 6 passes of ECAP. It was argued that this decrease was due to dynamic recovery of dislocation density during or after ECAP processes at $150^{\circ}C$. The strength assessment equation proposed by the authors in the previous paper was shown to be very accurate. This argument was supported by comparing the results of conventional tensile test with those of SP test. It was also pointed that the Rockwell har(3ness value seemed to be able to represent the strength in the transverse direction.

• Journal of Powder Materials
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• v.15 no.6
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• pp.482-488
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• 2008

The indentation technique has been one of the most commonly used techniques for the measurement of the mechanical properties of materials due to its experimental ease and speed. Recently, the scope of indentation has been enlarged down to the nanometer range through the development of instrumentations capable of continuously measuring load and displacement. In addition to testing hardness, the elastic modulus of submicron area could be measured from an indentation load-displacement (P-h) curve. In this study, the hardness values of the constituent phases in Ti($C_{0.7}N_{0.3}$)-NbC-Ni cermets were evaluated by nanoindentation. SEM observation of the indented surface was indispensable in order to separate the hardness of each constituent phase since the Ti($C_{0.7}N_{0.3}$)-based cermets have relatively inhomogeneous microstructure. The measured values of hardness using nanoindentation were ${\sim}20$ GPa for hard phase and ${\sim}10$ GPa for binder phase. The effect of NbC addition on hardness was not obvious in this work.

• Journal of Periodontal and Implant Science
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• v.35 no.4
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• pp.891-905
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• 2005

The present study was performed to evaluate the effect of tetracycline-HCL on the change of implant surface microstructure according to application time. Implant with pure titanium machined surface. HA-coated surface and TiUniteTM surface were utilized. Implant surface was rubbed with 50mg/ml tetracycline-HCL solution for $\frac{1}{2}min.$, 1min., $1\frac{1}{2}min.$, 2min., and $2\frac{1}{2}min.$ respectively in the test group. Then, specimens were processed for scanning electron microscopic observation. The results of this study were as follows. 1. Both test and control group showed a few shallow grooves and ridges in pure titanium machined surface implants. There were not significant differences between two groups. 2. In HA-coated surfaces, round particles were deposited irregularly. The roughness of surfaces conditioned with tetracycline-HCL was lessened and the cracks were increased relative to the application time. 3. The anodic oxidized surfaces showed the craterous structures. The surface conditioning with tetracycline-HCl didn't influence on its micro-morphology. In conclusion, the detoxification with 50mg/ml tetracycline-HCL must be applied respectively with different time according to various implant surfaces.

• Maxillofacial Plastic and Reconstructive Surgery
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• v.13 no.3
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• pp.252-264
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• 1991

The purpose of this study was to compare the response of adjacent tissue and new bone formation after implantation by different methods of subperiosteal using using Proplast I and II in rabbit mandible. Microstructure of Proplast I and II was observed by scanning electron microscope. And the implantation procedure was carried out by dividing into tow groups, A and B. a group consisted of subperiosteal graft on the cortex, and the other B group was made up onlay graft following artificial decortication in the madibular body of rabbit. The experimental animals were sacrificed on the 1st, 2nd, 4th and 8th week after grafting for macroscopic and histopathologic examination. The samples extracted at the 6th postgrafting week were also used for biometric test. The result ere as follows : 1. By scanning electron microscopic observation, pore size was $50{\sim}180{\mu}m$ in the Proplast I and $100{\sim}220{\mu}m$ in Proplast II. 2. Macroscopically, infection of the graft site, deformation and displacement of the implanted materials were not observed in all experimental groups. 3. In the tissue response, infiltration of inflammatory cells and multinucleated giant cells were observed from the 2nd to the 8th week in Proplast I. Inflammatory cells decreased in number from the 2nd week in Proplast II suggesting that Proplast II is better than Proplast I. 4. Bone formation was not observed until the 8th week in the group A, but new bone formation from the surrounding graft bed and the periostium was appeared from the 4th week in the group B. 5. The maximum mean values of shear stress mere serially $65.5gf/mm^2$ in Proplast II of group B, $32.9gf/mm^2$ in Proplast I of group B, $17.0gf/mm^2$ in Proplast II of group A, and $15.7gf/mm^2$ in Proplast I. of group A.

• Journal of the Korea Institute of Building Construction
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• v.16 no.4
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• pp.313-320
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• 2016

The aim of this study is to look into the metakaolin replacement ratio of blast furnace slag based alkali activated slag mortar and its mechanical characteristics according to changes in stimulant concentration. Metakaolin has high fineness, and therefore the fluidity becomes lower as the replacement ratio becomes higher. So in this study, a sufficient value of mixing water was provided to secure fluidity for the characteristic experiment, and a different W/B was derived for each specimen in order to make the fluidity identical. A characteristic experiment was conducted according to the mol concentration of NaOH, which was used as the mixing water that affects fluidity. Additionally, compressive strength measurement, observation of inner microstructure through SEM, acid resistance experiment, and neutralization resistance was conducted. The results of this study revealed that for a high concentration NaOH solution to have even fluidity, a high W/B is necessary, and the functions were enhanced, not degraded.

• Journal of Advanced Marine Engineering and Technology
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• v.37 no.2
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• pp.135-143
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• 2013

Friction Stir Welding (FSW) was developed, it is successfully commercialized in the field of transportation vehicles. In this study, we analyzed the defects of A2024-T4 alloy using non-destructive test of radiograph, ultrasonic, electrical conductivity and destructive test of microstructure observation, tensile strength. As the results of experiment, mapping of defects was obtained. Fine defects which were not detected in radiograph test were detected in ultrasonic test, and it enabled efficient detection of defects by difference of sound pressure and color. The values of electrical conductivity was decreased as amount of defects was increasing. Joint efficient of defect-free weldment that found by non-destructive and destructive test was 91%. Therefore it was considered that non-destructive test of friction stir welded A2024-T4 Alloy was an efficient method.

• Korean Journal of Crystallography
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• v.9 no.1
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• pp.64-70
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• 1998

Porous body was prepared from coal fly ash 70 wt%0clay 30 wt% slip using DCC(Direct Coagulated Casting) method. Effect of the specific gravity of the slip on the pore size and distribution of the sintered body was examined by the SEM observation of microstructure and mercury porosimetry measurement of the pore size distribution. Average pore size of the porous sintered body was about 2.5μm for all slips with specific gravity of 1.55, 1.60 and 1.65g/cm3, respectively. Sintered body prepared from the slip of specific gravity of 1.60g/cm3 have the narrowest pore size distribution. slip of specific gravity of 1.55g/cm3 shows broader pore size distribution due to slow gellation process. Slip of specific gravity of 1.65g/cm3 required large amount of deflocculant and showed large variation of the viscosity with addition of coagulant which resulted in very unstable slip properties.

• Journal of Periodontal and Implant Science
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• v.37 no.2
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• pp.265-275
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• 2007

The present study was performed to evaluate the effect of Tetracycline-HCI on the change of implant surface microstructure according to application time. Implants with thermal dual acid etched surface were utilized. Implant surface was rubbed with $50mg/m{\ell}$ Tetracycline-HCI solution and sterilized saline for O.5min, 1min, 1.5min, 2min, 2.5min and 3min. respectively in the test group. Then, specimens were processed for scanning electron microscopic observation and measured surface roughness by optical interferometer. The results of this study were as follows. 1. The thermal dual acid etched surfaces showed many small peaks and valleys distributed overall surface. 2. The surface conditioning with Tetracycline-HCI and saline didn't influence on its micromorphology. In conclusion, the implant with thermal dual acid etched surface has a protective micromorphology from the detoxification with $50mg/m{\ell}$ Tetracycline-HCI and a scrubbing with cotton pellet. Therefore, the detoxification with $50mg/m{\ell}$ Tetracycline-HCI is an effective method for peri-implantitis in case implants with thermal dual acid etched surface.